In conventional vehicle automatic transmissions of the torque converter type, a driving shaft extends from the torque converter into the transmission housing to a unit having one or more clutch drums around which are arranged either single-wrap or double-wrap brake bands. It is the function of the brake band, through the application of suitable hydraulic controls, to effect gear changes and control the direction of rotation of the output shaft from the transmission to the differential for the driving wheels of the vehicle.
The present invention is an improvement in the anchor or reaction bracket of a transmission brake band and will be described in an embodiment intended to be utilized with a single-wrap brake band. However, the embodiment so described in this patent application is intended to be illustrative and is not intended to be limiting upon the use of this invention with transmission brake bands of all designs and styles.
Single-wrap brake bands are currently available in two distinct styles. The most commonly known single-wrap brake band is usually formed from a strip of sheet steel or similar material, having at its ends brackets formed from separate forgings, castings or stampings. The brackets are suitably secured to the strap of material by spot welding or similar methods as shown in U.S. Pat. No. 3,732,954. More recently, a unitary single-wrap brake band has been designed which utilizes a single piece of material wherein the brackets are extruded or formed from double thicknesses of the base metal at the ends of the strap member. An example of a brake band of this type of structure is disclosed in U.S. application Ser. No. 546,161 a parent application to this application, now allowed as U.S. Pat. No. 5,078,237.
Regardless of how the brake band and bracket members are formed, it is a requisite that each brake band have an actuation or apply end for receiving an apply piston and a reaction or anchor end which operatively receives a reaction member located in the transmission. Various types of automatic transmissions utilize different types of reaction members. Some reaction members may be of the tangential type which comprise a stationary plunger or stop member acting against the anchor end of the brake band, while other reaction members may be the reaction pin type where the pin is positioned perpendicular to the clutch drum and strap member and extends into a reaction opening located in the anchor bracket of the brake band.
Where a reaction pin is used as the reaction member in the transmission band, a "volcano" type reaction bracket is commonly provided to engage the reaction pin. A typical volcano bracket consists of an extruded opening extending radially outwardly from the reaction bracket of the band. Alternatively, a bushing secured to the bracket may have a reaction opening formed therein to receive the free end of the reaction pin, thus providing the anchored end of the brake band during use of the band in the automatic transmission. The opposite or apply end of the band is provided with an apply bracket for engaging the end of the apply plunger in the transmission. The apply plunger is hydraulically controlled to urge the apply end of the band towards the anchor end and thereby tighten the brake band around the clutch drum, thus stopping the rotation of the drum or otherwise altering the rotation of the drum or other member to change the gear ratio or alter the direction of rotation of the output shaft. Due to the high repetitive forces encountered by operation of a transmission brake band, the close tolerances required for proper function between the free end of the reaction pin and the opening of the volcano are critical. Many problems have been encountered in which the volcano opening fails prematurely during testing or operation of transmission. For instance, if the reaction pin is not fully engaged with the volcano opening the open edges of the volcano may chip, splinter, and crack.
U.S. Pat. No. 5,078,237 approaches the stress failure problems of such volcano brackets by providing a single piece brake band with an anchor embossment extruded from a double thickness of the strap material to produce a volcano type reaction bracket at one end of the brake band. The strap material is folded upon itself to form the double-layer and the volcano opening is formed by piercing the double layer of material to extrude the layers and form a tapered opening. The two layers of strap material are then secured together by clinch fastening, spot welding or other adequate means.
While the extruded volcano opening has provided for enhanced strength characteristics and has significantly reduced the number of stress failures in such volcano anchor brackets, it remains desirable to further reduce the risk of failure of volcano reaction openings. Problems with stress fractures and failure are still encountered, especially in situations where the reaction pin is not fully inserted through the volcano opening and forces are exerted at the upraised edges of the volcano opening.
Another structure designed to overcome the deficiencies of the volcano-type reaction openings is found in Canadian Patent No. 1,248,884 issued to one of the co-inventors herein. The Canadian '884 patent discloses an anchor bracket which is provided with a circular opening adapted to receive a reaction pin that is located generally perpendicular to the band. The reaction pin engages the forward edge of a pocket which is formed in a transverse ridge of the anchor bracket. The rearward edge of the pocket, however, provides little possibility of engagement with the reaction pin, due to the nonplanar shape of the ridge. Thus, the reaction opening found in the Canadian patent is deficient if the brake band must be designed to support a load in any direction other than the forward direction. The Canadian structure remains sensitive to the depth of the location of the reaction pin if loads are applied in any direction other than forward.
Yet another anchor structure is found in U.S. Pat. No. 5,083,642 which discloses a separate anchor bracket having an upraised channel-like surface surrounding the reaction opening. The anchor bracket is secured to the strap by conventional means such as spot welding or riveting along the sides of the bracket and band. Such a structure however has developed a tendency to flatten out or stretch under a load taken in the direction of the unsecured edges of the bracket. Thus, a need is still present for an anchor member which can receive an anchor or reaction pin and carry a load exerted in any direction without need for reinforcement to prevent distortion of the bracket.
It is yet another object of this invention to support a load applied to the brake band from any direction without the need for preloading the brake band which has the potential for interfering with band installation.
It is a further object of this invention to provide an anchor assembly for a transmission band wherein the reaction opening can be provided without overly stressing or distorting the surrounding material.
It is a final object of this invention to provide a reaction bracket having enhanced strength characteristics designed to overcome the possibility of premature failures of the brake band.
The present invention achieves these goals by increasing the strength of the bracket and reducing the stress on the reaction opening so that premature failure of the bracket is quantitatively lessened.